1. Field of the Invention
The present invention relates to a jitter correcting system in a video reproducing apparatus. More specifically, the present invention relates to a pseudo television composite signal generating apparatus for use in such a jitter correcting system in a video reproducing apparatus.
2. Description of the Prior Art
When a television image is reproduced on the screen of a television receiver in accordance with the composite video signal reproduced by a video reproducing apparatus, such as a video disc player or the like, a jitter is liable to be caused and as a result of weaving of the television image along the vertical direction. Such jitter occurs in accordance with the phase difference caused between the phase of the composite video signal applied from a video reproducing apparatus to a television receiver and that of a horizontal deflection signal obtained from an automatic frequency control normally included in such a television receiver generated upon extraction of the horizontal synchronizing signal in the said composite video signal. Such a phase difference between a composite video signal and a horizontal deflection signal is caused in a television receiver, because a video reproducing apparatus reproduces a composite video signal from a television signal recorded medium with relatively low accuracy in terms of the reproduced signal phase determined by a mechanical structural characteristic thereof, whereas an automatic frequency control serves to stabilize the frequency of a horizontal deflection signal in an electronic manner. Accordingly, it is possible to reduce the jitter appearing on the screen with relative simplicity when a television receiver has been structured such that the time constant of the automatic frequency control can be externally adjusted with ease to a smaller value. However, as is the case of television receivers widely used nowadays in homes, the time constant of the automatic frequency control cannot be adjusted with ease by the user and the receivers are often used as a monitor television receiver for the purpose of reproduction of the video signal obtained from a video reproducing apparatus for domestic use, such as a video disc player or the like. Thus the above described approach for changing the time constant of the automatic frequency control requires that a monitor television receiver be remodelled for the purpose; however, this cannot be adopted mainly from the viewpoint of service of domestic television receivers.
A prior art of interest to the present invention is U.S. Pat. No. 3,681,522, issued Aug. 1, 1972 and entitled "System for Minimizing Fluctuations of Television Signal", which discloses an improved jitter correcting system that is capable of eliminating with simplicity such a jitter in a monitor television receiver without any remodeling of the receiver. According to the art disclosed therein, a reproduced composite video signal obtained from a video reproducing apparatus is not directly applied to a monitor television receiver but rather the reproduced composite video signal is adapted to undergo phase modulation of the horizontal synchonizing signal in the said composite video signal so as not to cause the above discussed phase difference between the composite video signal and the horizontal deflection signal in the receiver and the resultant composite video signal with the phase modulated of the horizontal synchronizing signal is applied to a monitor television receiver. In other words, the referenced United States Patent is, as a matter of principle, aimed to phase modulate the horizontal synchronizing signal of the reproduced composite video signal by the amount corresponding to the phase difference between the composite video signal to be applied to a picture tube of a monitor television receiver and an output signal from an automatic frequency control included in the said monitor television receiver, so that the phase difference caused by the video reproduction apparatus is compensated for in advance. In comparison with the above described approach for changing the time constant of an automatic frequency control in a monitor television receiver with the approach for compensating in advance for the phase difference in question, the latter approach is much more advantageous in that the latter approach can compensate for the phase difference in question completely, while the former approach cannot make the phase difference in question be zero.
In the jitter correcting system disclosed in the referenced United States Patent, in order to minimize a jitter, adjustment should be made of the system such that a modulating signal for phase modulating the horizontal synchronizing signal of the reproduced composite video signal copes better with the frequency characteristic of the automatic frequency control included in the monitor television receiver. In the event such a frequency characteristic of an automatic frequency control in a receiver is known in advance, it is easier to design an adjusting means in such a jitter correcting system so as to be adapted to such a frequency characteristic of the automatic frequency control. However, since as a matter of practice television receivers now widely used in homes exhibit a variety of frequency characteristics in the automatic frequency control thereof, it is not always easier to provide an adjusting means in such a jitter correcting system which is adapted to the respective cases. The referenced United States Patent fails to disclose any of such an adjusting means adaptable to a variety of frequency characteristics of the automatic frequency control in different television receivers. Thus, the referenced United States Patent has room for improvement in practising the same.